In recent years, ULTRAVIOLET-curable photosensitive resin compositions have been abundantly used in a wide variety of fields, such as coating materials, adhesives, and resists, because of various reasons including high productivity, low-pollution, and energy-saving properties. In the field of processing printed wiring boards, cover materials for various ink systems, such as solder resist ink, are being replaced from the conventional screen-printing system to ULTRAVIOLET-curable compositions. In addition, remarkable progresses in electron technologies allow the conventional rigid substrates to be substituted by flexible substrates because of advancing high-density and weight-saving technologies.
In general, in the case of using ink as a covering material, as the characteristics of the covering material after curing, the covering material used for a rigid substrate does not need pliability so much, but in the case of using a covering material for a flexible substrate, the cover material has been desired to be high in pliability in order to employ the characteristic features of the flexible substrate.
Further, JP 07-207211 A describes a curable photosensitive material including an epoxy resin, an unsaturated group-containing polycarboxylic acid resin provided as a reaction product of an unsaturated group-containing monocarboxylic acid and an carboxylic acid anhydride, and a photopolymerization-initiator. However, such a material has poor folding-endurance characteristics because of a lack in sufficient flexibility or pliability. Besides, a trouble such as the substrate warps after processing occurs. An improvement in such a trouble has been demanded in various fields. For this reason, as shown in JP 2004-294882 A, a composition containing a siloxane polyimide as a main component for expressing low elasticity has been proposed. In those compositions, warping of a substrate after processing may be decreased, but the compositions may cause problems of high price and poor storage stability of the composition at room temperature.    Patent Document 1: JP 07-207211 A    Patent Document 2: JP 2004-294882 A